kerberos tests pass on all Node versions (including Node18) on ubuntu20, but fail on Node18 on rhel8.

Some thoughts

• kerberos relies on krb5 and krb5_gssapi.  we should check the versions of these dependencies on ubuntu20 and rhel8 in case we're incompatible with an older version of these libraries
• we should check the kerberos configuration for these libraries on each distro.  unlikely, since kerberos passes on Node<18 on rhel8 but worth investigating.